No, Pershing has had its crew disembark feature removed as a quick implementation for Relic to limit Heavies to one per player.
What's OP about USF Ambulances now? :/
The problem with Priest and Calliope having crew is that one can have them without paying the upkeep for them...
There is still a cost of at least 280 fuel for both players to have at least one Calli.
A player leaving their crew next to the priests/callis as a mean to bypass upkeeps just begs the opponent to kill the crew and take over the tanks themselves. Additionally, this will force even more micro on the USF player, and one cannot micro everything. Going slightly over the popcap using decrew has been underlined as a valid tactic as denoted by Relic themselves.
Really, this is more of a L2P issue, and you do seem to exaggerate the issue at hand a bit, which reminds me of you attempting to define the in-game term "fortification" recently. I haven't read anything about de-crewing being OP since the beta of WFA, when crews were able to instantly crew/decrew tanks in combat, messing up with the enemy's targetting..